There is an increasing demand for many plastic products to be biodegradable. One product that has been the subject of attention is the tampon applicator which conveniently should be water flushable water dispersible and biodegradable. Difficulties have been encountered in producing starch based polymers particularly for injection moulding. The molecular structure of the starch is adversely affected by the shear stresses and temperature conditions needed to plasticise the starch and pass it through the extrusion die. For most products foaming has to be avoided and this generally requires attention because of the water content of the starch. Foaming has been avoided by degassing the melt prior to exiting the die as suggested in U.S. Pat. Nos. 5,314,754 and 5,316,578. The latter patent also avoids adding water to the starch. As explained in U.S. Pat. No. 5,569,692 by not drying starch and avoiding the addition of water the starch can be processed at temperatures between 120° C. and 170° C. because the water bound to the starch does not generate a vapour pressure such as to require high pressures.
Another approach to improving the melt processability of starch is to provide an additive as in U.S. Pat. No. 5,362,777 which reduces the melting point of the starch. The additive is selected from dimethyl sulfoxide, a selection of polyols and amino or amide compounds.
U.S. Pat. No. 5,043,196 discloses a high amylose starch for injection moulding.
U.S. Pat. No. 5,162,392 to an injection moldable corn starch and LDPE biodegradable polymer.
In order to produce starch polymers for particular applications they have been blended with a range of other polymers. Biodegradable blown films are disclosed in U.S. Pat. No. 5,322,866 which blends raw starch, polyvinyl alcohol and talc with glycerol and water. U.S. Pat. No. 5,449,708 discloses compositions of starch ethylene acrylic acid and a salt of stearic acid plus a glycerol based lubricant. Flexible and clear transparent sheets are disclosed in U.S. Pat. No. 5,374,304. These are composed of a high amylose starch and a glycerol plasticizer. The use of starch in conjunction with high amylose or modified starches has also been proposed. U.S. Pat. Nos. 5,314,754, and 5,316,578 both suggest the use of modified starches including hydroxypropyl substituted starches. Hydroxypropylation reportedly increases elongation at break and burst strength and improved resilience in the polymers.
Patent WO00/36006 discloses biodegradable water soluble formulations using a major amount of modified starch and a minor amount of a water soluble poly vinyl alcohol. These formulations are thermo formable but there are no examples of injection mouldable compositions.
Biodegradable tampon applicators are the subject of a number of patents. U.S. Pat. No. 5,759,569 discloses trans polyisoprene as biodegradable polymer for diaper top sheets and tampon applicators.
Patent applications 2003/0036721 and 2003/0040695 relate to flushable tampon applicators comprised of polyethylene oxides and other components.
U.S. Pat. No. 5,002,526 discloses a polyvinyl alcohol tampon applicator.
U.S. Pat. No. 5,350,354 discloses a tampon applicator composed of starch or modified starch, at least 5% of a plasticizer such as glycerol and water.
U.S. Pat. No. 5,804,653 to a moldable polyvinyl alcohol composition for tampon applicators.
It is an object of this invention to provide an injection mouldable biodegradable polymer which can be processed have acceptable properties for intended uses such as tampon applicators.